254SMo steel (S31254, 00Cr20Ni18M06CuN) is one of the earliest super austenitic stainless steels developed in the 1970s. It not only has good overall corrosion resistance in reducing media, but also has excellent resistance in chloride-containing media The performance of local corrosion such as pitting corrosion and crevice corrosion. At the same time, the strength of this steel is higher than that of general chromium nickel austenitic stainless steel due to the strengthening effect of nitrogen.
It is precisely because of these characteristics that 254SMo steel has become increasingly widely used, and it can also replace high nickel corrosion-resistant alloys in some applications.
Chemical composition and organizational characteristics of 254SMo
The solid solution state of 254SMo is a single austenite structure, but it is affected by the thermal history. For example, carbides and intermetallic phase compounds will precipitate in the heat affected zone during the cooling process of hot working and after welding, due to the carbon content in the steel It is very low, so it is mainly the X phase, α phase, β and other intermetallic phases and the precipitation of Cr2N is the TTP (temperature-time-precipitation) curve of 254SMo containing 0.21% N.
The kinetic curves of the intermetallic phase precipitation of 254SMo steel and the comparison results with the phases containing molybdenum (316) and high molybdenum (904L and 317LMN). It can be seen that the most sensitive temperature for the precipitation of inter-general phases in this steel is 800~900°C.
Because 254SMo steel has high chromium and molybdenum content and low nitrogen content, the sensitivity of intermetallic phase precipitation is higher than that of high-molybdenum austenitic stainless steel 904L (0OCr20Ni25Mo4.5Cu), 317LMN and low-molybdenum 316. For this reason, appropriate measures should be taken to prevent the precipitation of intermetallic phases during 254SMo hot forming and welding.
Posted by stainless steel pipe fittings supplier kaysuns